According to one aspect of the present invention a method for control of a multi-variable process, comprises deriving a multi-dimensional representation of the process variables according to individual coordinate axes, defining a feasible region of the process-variables based on sets of values for the process-variables accumulated respectively in relation to multiple operations of the process, defining for each process variable a range due to the values of the other process variables, within which the value of that variable is to lie in order for operation to remain within the feasible region, detecting in respect of each of the variables whether an alarm condition exists in which the current value of that variable lies outside the range defined for it, responding to the existence of said alarm condition to calculate change of the value or values of one or more of the variables required to rectify the alarm condition, and implementing the calculated change.
According to another aspect of the present invention a system for control of a multi-variable process, comprises means for deriving a multi-dimensional representation of the process variables according to individual coordinate axes, means for defining a feasible region of the process-variables based on sets of values for the process-variables accumulated respectively in relation to multiple operations of the process, means defining for each process variable a range due to the values of the other process variables, within which the value of that variable is to lie in order for operation to remain within the feasible region, means for detecting in respect of each of the variables whether an alarm condition exists in which the current value of that variable lies outside the range defined for it, and means responding to the existence of said alarm condition to calculate change of the value or values of one or more of the variables required to rectify the alarm condition, and means for displaying the calculated change.
The definition of the feasible region and the ranges of the process-variables in the method and system of the invention may be carried out using convex hulls or any other closed envelope embracing the data points represented respectively by the accumulated sets of values. A convex hull in orthogonal coordinates is a closed polygon that encloses all relevant data points of the two-dimensional space, whereas in parallel coordinates it is a pair of spaced linear curves that as between corresponding parallel axes, bound the region occupied by the lines that represent (in the parallel-coordinate space) those data points.
The current values of at least some of the process variables and said ranges defined individually for them, may be displayed in said multi-dimensional representation.